1. Field of the Invention
The present invention relates to a process for preparing methyl tertiary-butyl ether (hereinafter referred to as "MTBE") by the continuous reaction of an isobutylene hydrocarbon with methanol in the presence of a catalyst, giving a high yield.
2. Brief Description of the Prior Art
In recent years, pollution resulting from lead present in exhaust gases from internal combustion engines has become a big problem. Accordingly, regular type gasolines are entirely leadless at the present time, and premium type gasolines will sooner or later be made leadless. However, in order to make gasoline leadless without a big change in the mixing ratio of the base gasolines while maintaining the octane number of conventional gasolines, it is necessary to add an agent for increasing the octane number.
A number of agents for increasing octane number are already known. Among them, ethers having a branched chain type alkyl group were disclosed in the Third World Petroleum Congress, Sec. M, 397 (1951). It is known that, for example, methyl tertiary-butyl ether (MTBE), ethyl tertiary-butyl ether, and isopropyl tertiary-butyl ether have extremely high octane numbers.
It is known that MTBE can be prepared by the reaction of methanol and isobutylene in the presence of an acid catalyst. In particular, some processes have been proposed in which a strong acid type cation exchange resin is employed as the catalyst (for example, Japanese Patent Publication No. 34,803/1973, Published unexamined Japanese Patent Application Nos. 61,109/1974 and 58,006/1975 and U.S. Pat. No. 2,480,940). However, these conventional processes permit the extraction of acidic materials into the mixture of reaction products from the strong acid type cation exchange resins used during the reaction, so that a heating procedure is required in the distillation step in which the reaction products are separated. This heating procedure, however, produces undesirable effects in that a considerable degree of a reverse reaction from the MTBE product to the methanol and isobutylene occurs, thereby resulting in a decrease in the yield of the MTBE because of the presence of the tertiary carbon atom in the MTBE. Furthermore, products which contain acidic materials cannot be added as they are to fuel gasolines.
The present inventors have invented and already applied for a patent on an invention for the continuous process for preparing a tertiary alkyl ether from a lower primary alcohol and a tertiary olefin on an industrial scale and with good yield by carrying out the flashing and distillation operations after removal of the undesirable acidic materials from the reaction product mixtures by means of a solid particulate acid neutralizing agent (Japanese Patent Application No. 140,479/1976).
Furthermore, the present inventors have invented and already applied for another patent on an invention directed to a process which comprises reacting an olefin with a lower alcohol in an excessive amount with respect to the olefin used, removing the acidic materials by means of a solid particulate acid neutralizing agent, then removing the unreacted hydrocarbon by means of a flashing procedure, further distilling the distilled reaction mixtures to provide an azeotropic mixture of MTBE and methanol at the top of a distillation tower, recycling the azeotropic mixture to the first reactor where the olefin is reacted with the lower alcohol, and providing a high purity MTBE at the bottom of the distillation tower (Japanese Patent Application No. 123,154/1977).